FIG. 1 shows a known apparatus 10 for supporting a rotating shaft. To the left of the figure apparatus 10 is shown partly assembled, to the right fully assembled, and at the bottom of the figure is shown a single tilting pad 14 of the apparatus. Thus, apparatus 10 comprises: (i) a tubular housing 12 along the axis A′ of which in use of the apparatus a supported shaft (not shown) extends; (ii) carried by housing 12, and in use of the apparatus interposed between housing 12 and the supported shaft, five tilting pads 14 which extend in contiguous manner circumferentially around the shaft, each tilting pad being able to rock in known manner in the rotation of the shaft to accommodate vibration of the shaft; and (iii) interposed between each pair of adjacent tilting pads 14 a cylindrical retaining pin 20 for preventing circumferential movement of the pads around housing 12 due to rotation of the shaft. Indicated on the single tilting pad 14 shown at the bottom of FIG. 1 is the axis A of the pad. In known manner the radius R of each tilting pad 14 is somewhat smaller than the radius R′ of tubular housing 12, see the partly assembled apparatus to the right of FIG. 1. This is so that each tilting pad 14 is able to rock as required within housing 12 to accommodate vibration of the supported shaft.
FIG. 2 illustrates rocking of a tilting pad 14 in use of apparatus 10. A supported shaft (not shown) rotates anticlockwise as indicated by arrow 22. Friction between the shaft and pad 14 causes pad 14 to be urged against cylindrical retaining pin 20. Rocking of pad 14 would tend to take pad 14 from its position shown in solid line to its position shown in dotted line. However, such unfettered rocking is prevented by abutment with retaining pin 20.
As shown in the exploded portion of FIG. 2, in the solid line position of pad 14 the right hand side of the pad abuts and runs parallel to the left hand side of cylindrical retaining pin 20. Rocking of pad 14 from its solid line position to its dotted line position would tend to move the right hand side of the pad as shown. Such movement is of course prevented by retaining pin 20. Thus, in order to rock, pad 14 slips circumferentially a distance Df around tubular housing 12 in a clockwise sense, i.e. in a sense opposite to that of rotation of the supported shaft. Distance Df is the distance in the circumferential direction between the solid and dotted line positions of the radially outer edge 24 of the right hand side of pad 14. Finally, when pad 14 is called upon to rock back to its solid line position, this again results in pad 14 slipping circumferentially the distance Df around housing 12, but this time in an anticlockwise sense.
The slippage back and forth of pad 14 circumferentially around housing 12 causes friction between the abutting faces of pad 14 and housing 12 with the result that there is premature wearing of the pad and housing.